1. Field of the Invention
This invention relates in general to magnetic storage systems, and more particularly to a method and apparatus for providing a marker for adaptive formatting via a self-servowrite process.
2. Description of Related Art
Magnetic recording systems that utilize magnetic disk and tape drives constitute the main form of data storage and retrieval in present-day computer and data processing systems. In the recording process, information is written and stored as magnetization patterns on the magnetic recording medium. Scanning a write head over the medium and energizing the write head with appropriate current waveforms accomplish this recording process. In a read-back process, scanning a read sensor over the medium retrieves the stored information. This read sensor intercepts magnetic flux from the magnetization patterns on the recording medium and converts the magnetic flux into electrical signals, which are then detected and decoded.
Continually increasing storage capacities in hard disk drives require innovations in magnetic hard disk drive design. One area of concern is the need for precision manufacturing. Hard disk drives store data in concentric tracks, and the density of those tracks has increased along with linear bit density over time. To read and write data, the disk drive head must remain accurately centered on a selected track. At today's track densities, the head must stay centered on the narrow tracks to within a staggering tolerance of one-millionth of an inch or less. To achieve this level of precision, the head must read position information along the track that is permanently written onto the disk. The position information is used by a precision electronics control system that servos the recording head onto the track.
The process by which the position information is written onto the disks is referred to as servowriting and is performed only once—during the manufacture of the device. The information remains on the disk for the life of the product. The machines that write these servo patterns—called servowriters—must be very precise instruments.
Traditional servo writing has been performed in a clean room environment with external sensors invading the head disk assembly to provide the precise angular and radial position information to write the servo patterns. For example, an external clock head was typically disposed on the disk outer diameter. This provided the angular information used to write the servo patterns. While such instruments have been satisfactory to set the patterns in the past, today's increased track density has become so precise that the mechanical vibration of the file (relative to these external sensors) as well as other factors can limit the accuracy or increase the complexity of these systems.
A more precise servowriting technology has been developed to overcome the problems associated with the traditional servo writing process. The new approach uses servowrite self-timing technology. The clock heads used in traditional servowriters is replaced with an electronic non-invasive process to create the time alignment of servo patterns between adjacent tracks.
A digital signal processor executing a predetermined mathematical algorithm is used to accomplish the time alignment. In this method, the hard disk drive generates its own timing information while the drive is being servo written, using only the product data head. The patterns are self-propagated and aligned by a digital signal processor (DSP), resulting in a substantial increase in time alignment over other servowriting methods and significantly improved performance, quality, and reliability.
The self-servowrite process eliminates mechanical vibrations associated with external clocking while significantly improving servo pattern time alignment. This results in fewer servo errors—and thus fewer write inhibits—to improve drive performance. The improved time alignment also enables a reduction in the size of the sector fields, thereby increasing data capacity. The self-servowrite process also eliminates external invasive clock heads, which can damage the drives during manufacture. Thus, the drive leaves the manufacturing facility with a clean bill of health, having been assembled and tested in a manner to preserve its quality and integrity.
Improved time alignment in the servo pattern fields means fewer servo substitutions, which further increases data reliability. Additionally, the self-servowrite process includes in-process algorithms to detect and correct servowriter errors as they occur. The result of this monitoring of the servowriting process (catching and correcting errors “on the fly”) is that disk drives are servo written with fewer errors. This improves product quality and makes the manufacturing process more efficient—all of which can reduce the cost for end users.
Nevertheless, for adaptive formatting, wherein the number of available data tracks can vary, the number of tracks to be formatted must be determined. Currently, determining the number of available tracks from the self servowrite process requires a trial and error process or requires that the track count be sent ahead from the servowriter to the function test station.
It can then be seen that there is a need for a method and apparatus for identifying the number of tracks written on the surface and thus determine the appropriate format to use in the drive.